One of the central paradigms of modern drug discovery is high throughput screening (HTS), which is the heart of lead discovery programs in the pharmaceutical industry. HTS involves the execution of a large number of assays where hypothetical drug targets are exposed to a library of small molecules. As these programs have developed, the number of assays that need to be performed has increased dramatically. Combinatorial chemistry has been applied to make an extraordinary variety of small molecule themes, and numerous potential targets have emerged from functional genomics.
In view of the foregoing, an ongoing need for improved screening technology has developed in order to hold back the cost and time consumption requirements of prior HTS systems. The introduction of high-density, low volume formats addresses both issues. The industry has gradually been incorporating miniaturized microtiter plate based technology. The necessary liquid handling and readout devices for 384, 1536 and 3456-well plates are commercially available. The first choice tends to be 1536 well plates, but 3456 and 384 well plates are also used, the latter often being preferred for cellular assays. Assay volumes in 384 well plates range down to 10 microliters and for 1536 well plates down to 1 microliter. Applications of 9600 well plates with assay volumes down to 0.2 microliters have been reported.
The assays employed in HTS fall into two categories: homogeneous and heterogeneous assays. The former involve only fluidic additions, incubations and reading. In addition to these operations, heterogeneous assays may require washing, filtering or centrifugation. Each category of HTS has its own pros and cons. While heterogeneous assays take more time to perform and require more complex robotics to automate, they generally provide higher quality data and are easier to develop. Heterogeneous assays can be developed for any analyte for which either a binding protein or an antibody exists. This is very important considering that assay development is often the rate limiting step in the lead discovery process.
An alternative approach towards further assay miniaturization is microfluidics. There have been numerous attempts to provide the valving and the mixing functionality necessary to enable an entire assay to be performed within a microfluidic system. Practically all of these prior attempts at providing a functional microfluidic system require the continuous flow of a fluid through a channel of a microfluidic device. Consequently, several non-traditional pumping methods have been developed for pumping fluid through a channel of a microfluidic device, including some which have displayed promising results. However, the one drawback to almost all pumping methods is the requirement for expensive and/or complicated external equipment, be it the actual pumping mechanism (e.g., syringe pumps), or the energy to drive the pumping mechanism (e.g., power amplifiers). The ideal device for pumping fluid through a channel of a microfluidic device would be semi-autonomous and would be incorporated totally at the microscale.
The most popular method of moving a fluid through a channel of a microfluidic device is known as electrokinetic flow. Electrokinetic flow is accomplished by conducting electricity through the channel of the microfluidic device in which pumping is desired. While functional in certain applications, electrokinetic flow is not a viable option for moving biological samples through a channel of a microfluidic device. The reason is twofold: first, the electricity in the channels alters the biological molecules, rendering the molecules either dead or useless; and second, the biological molecules tend to coat the channels of the microfluidic device rendering the pumping method useless. Heretofore, the only reliable way to perform biological functions within a microfluidic device was by using pressure-driven flow. Therefore, it is highly desirable to provide a more elegant and efficient method of pumping fluid through a channel of a microfluidic device.
It can be appreciated that one of the benefits of using microfluidic channels to perform assays is that only a small fraction of the liquid surface is exposed to the atmosphere. This reduces evaporation, which is a serious problem associated with low-volume microtitre plate assays. A few microfluidics-based HTS solutions are commercially available, but all require investment in specialized hardware for reagent introduction and readout. As such, it is highly desirable to provide a microfluidic system that is compatible with conventional microplate pipetting workstations.
Therefore, it is a primary object and feature of the present invention to provide a device and method for performing high throughput assays that utilize commercially available liquid handling robotics.
It is a further object and feature of the present invention to provide a device and method for performing high throughput assays that are simple and inexpensive.
It is a still further object and feature of the present invention to provide a method for performing a high throughput assay the may be performed more quickly than and with a fraction the fluids required in prior methods.
In accordance with the present invention, a device is provided for performing an assay. The device includes a plate structure having a channel therein. The channel has an input and an output. A plurality of ports are provided in the input of the channel.
The plate structure includes a plate having an upper surface. The channel is provided in a first microfluidic structure positioned on the upper surface of the plate. The first microfluidic structure includes an upper surface that is hydrophobic. The plate structure includes a second microfludic structure positioned on the upper surface of the plate. The second microfluidic structure defines a channel having an input and an output. The input of the channel of the second microfluidic structure has a plurality of ports. In addition, the output of the channel of the second microfluidic structure may include a plurality of output ports. The device may include a liquid dispensing instrument that extends along an axis. It is contemplated for the input of the channel to be axially aligned with the liquid dispensing instrument.
In accordance with a further aspect of the present invention, a device is provided for performing a high throughput assay. The device includes a plate and a plurality of microfluidic structures thereon. Each microfluidic structure defines a channel having an input and an output. At least one of the inputs and the outputs of the channels of the plurality of mircofluidic structures includes a first plurality of ports.
Each of the plurality of microfluidic structures includes an upper surface that is hydrophobic. It is contemplated for the plurality of microfluidic structures to be removable from the plate. Further, each of the outputs of the channels of the plurality of microfluidic structures may include a plurality of output ports. A liquid dispensing instrument deposits drops along a plurality of generally parallel axis. Each axis extends through a corresponding input of the channels of the plurality of microfluidic structures.
In accordance with a still further aspect of the present invention, a method of pumping fluid is provided. The method includes providing a microfluidic device having a channel therethough. The channel has a plurality of input ports and an output. The channel is filled with fluid and a pressure gradient is generated between the fluid at the input ports and the fluid at the output port such that the fluid flows through the channel towards the output. It is contemplated for the output of channel to include a plurality of output ports.
The pressure gradient is generated by depositing a reservoir drop of fluid over the output of the channel of sufficient dimension to overlap the output and by sequentially depositing pumping drops of fluid at the input ports of the channel. Each of the pumping drops has a predetermined radius. The reservoir drop has a radius greater than the radii of the pumping drops and greater than the predetermined radius of the output of the channel. The channel through the microfluidic device has a resistance and each of the pumping drops has a radius and a surface free energy. The reservoir drop has a height and a density such that fluid flows through the channel at a rate according to the expression:
            ⅆ      V              ⅆ      t        =            1      Z        ⁢          (                        ρ          ⁢                                          ⁢          gh                -                              2            ⁢            γ                    R                    )      wherein: dV/dt is the rate of fluid flowing through the channel; Z is the resistance of the channel; ρ is the density of the reservoir drop; g is gravity; h is the height of the reservoir drop; γ is the surface free energy of the pumping drops; and R is the radius of the pumping drops.